Method and system of non-destructive testing for composites

ABSTRACT

Method and system are disclosed for characterizing and quantifying composite laminate structures. The method and system take a composite laminate of unknown ply stack composition and sequence and determine various information about the individual plies, such as ply stack, orientation, microstructure, and type. The method and system can distinguish between weave types that may exhibit similar planar stiffness behaviors, but would produce different failure mechanisms. Individual ply information may then be used to derive the laminate bulk properties from externally provided constitutive properties of the fiber and matrix, including extensional stiffness, bending-extension coupling stiffness, bending stiffness, and the like. The laminate bulk properties may then be used to generate a probabilistic failure envelope for the composite laminate. This provides the ability to perform non-destructive QA to ensure that individual lamina layup was accomplished according to specifications, and results may be used to identify a numerous laminate properties beyond purely structural.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is a 35 U.S.C. 371 application of PCT/US2013/33187filed Mar. 20, 2013 claims priority to U.S. Provisional Application Ser.No. 61/613,482, entitled “Method and System of Non-Destructive Testingfor Composites,” filed Mar. 20, 2012, with the United States Patent andTrademark Office.

BACKGROUND OF THE INVENTION

1. Technical Field of Invention

The invention disclosed and taught herein relates generally to a methodand system of automatically identifying and characterizing compositelaminate structures, or laminates, using ultrasonic non-destructivetesting (NDT) techniques. More specifically, the invention disclosedherein relates to a method and system of automatically detecting eachlayer, or ply, of material in a laminate and determining the bulkproperties of the laminate based on the properties of the constituentplies in order to generate a failure envelope for the laminate. Theinvention disclosed and taught herein also relates to a method andsystem of simulating an ultrasonic scan of the individual plies of alaminate.

2. Description of Related Art

Composite laminates, or laminates, are typically composed of individuallayers of materials that have directionally dependent materialproperties. Each layer is commonly known as a lamina or ply, and theplies are combined in layers to create a bulk structure that forms thelaminate. Knowledge of the individual lamina configuration is importantbecause of the significant effect each lamina has on the finalproperties of the laminate. For example, in unidirectional fiberorientation plies, the ply is considerably stronger in the fiberorientation direction than in any other direction. The choice oforientation, thickness, stacking sequence, or other property of a laminawithin the final composite, will drastically alter the final processedmaterial properties of the laminate.

Composite laminates are used extensively in a variety of structuralapplications and in numerous industries. For example, carbon fiberreinforced polymers/plastics (CFRP) are a commonly-used type ofcomposite laminates in the aerospace, automotive and other industries.Although CFRPs can be relatively expensive, their superiorstrength-to-weight ratios make them more desirable than other types ofmaterials. This is reflected by the widespread and steadily increasinguse of CFRP components in fixed and rotary wing airframes, for example.Alternatively, a large industry exists that implements alternativereinforcements sacrificing the ultimate tensile strength for otherdesign parameters such as cost, processing ease, etc. Commonly employedfibers may include, but are not limited to, fiberglass, Kevlar, aramid,and other synthetic fibers, as well as a wide variety of natural fibersused as fillers.

Manufacturing carbon fibers usually involves a process where a singlecontinuous carbon fiber filament is constructed with a diameter ofroughly 0.005 mm to 0.010 mm. For the type of high quality products usedin aerospace applications, a typical fiber diameter will be on the orderof 0.005 mm. These filaments are 93% to 95% carbon and have a linearmass of roughly 6.6 grams per meter (g/m). Individual filaments are thenwound into a “tow” (i.e., thread or ribbon) that may then be used forvarious applications. Typical tows have between 3,000 and 12,000filaments depending on the product application. A 3,000-filament tow hasa linear mass of about 0.2 g/m and can be between 0.375 mm and 1.5 mmwide and between 0.2 mm and 0.05 mm thick. By comparison, the diameterof an average piece of thread is approximately 0.375 mm for a3,000-filament thread.

The tows may be woven into a pattern and then impregnated with resin toform an individual lamina that may then be stacked on other laminas tocreate a composite laminate layup. The main geometries for an individuallamina are: Percent Warp=percent of orthogonal fibers by weight (where0% means fibers are unidirectional, and 50% means fibers are woven);Areal Density=g/m² of fiber in a given lamina; Thread Count=number ofindividual fiber threads in an individual tow; Tow Width=width in mm ofan individual tow; Layer Thickness=thickness of an individual lamina inmm. In contrast, the main geometries for a completed composite layupare: number of laminas, fiber orientation of individual lamina, thelamina type (i.e., woven versus non-woven, woven type, material makeup),and layup method of individual layers.

The need to repair and modify laminated composites has stretched thecapability of existing non-destructive inspection (NDI) techniques.Specifically, to properly modify or repair laminated composites,sufficient fidelity of the underlying microstructure of the compositeplies is required to understand the baseline (i.e., unmodified,unrepaired) structure, identify and quantify any as-installedmodifications, and analyze the as-installed components for FAA,automotive, and other industry certifications.

In addition, the manufacturing process for composite laminates, as forother materials, inherently includes some variability that can affectthe performance of the final part. As such, it is desirable to accountfor these manufacturing uncertainties and tolerances when quantifyingthe expected structural response of composite laminates. It is alsodesirable to quantify the impact of manufacturing defects and varyingmaterial properties on a composite laminate's performance. Conversely,if the configuration of a composite laminate can be determined withinsome degree of confidence, it would be desirable to quantify theexpected structural response and life expectancy of that laminate.

Having the ability to detect manufacturing, installation, or usageeffects on a composite laminate, with resolutions on the order ofindividual lamina dimensions and as a function of affected lamina layer,may also minimize modification and maintenance design conservatism orsafety margins, leading to reduced manufacturing, installation, and testcosts.

The ability to quantify a composite laminate's expected structuralresponse would be particularly useful where the manufacture's data andinformation about the composite laminate are limited or perhapsunavailable. The problem is compounded by the need in many instances toascertain the composite laminate's as-fabricated structuralcharacteristics, including stiffness, failure envelope, and the like,without performing destructive testing.

Accordingly, what is needed is a system and method for identifying andcharacterizing a composite laminate's internal structure usingultrasonic NDT techniques. More particularly, what is needed is a systemand method for quantifying the composite laminate's expected structuralresponse based on the assessed properties of the individual laminas.

SUMMARY OF THE INVENTION

Embodiments of the invention provide a method and system forcharacterizing and quantifying composite laminate structures. The methodand system can take a composite laminate of generally unknown ply stackcomposition and sequence and determine various information about theindividual plies, such as the number of plies, ply stack sequence, plyorientations, and the like, based on simulated or actual datarepresenting a scan of the composite laminate. This information, alongwith information regarding the types of plies and the ply constitutiveproperties, such as resin type, cure cycle, and specific type of fiber,may then be used to determine a ply failure load. The information aboutthe plies may also be used to derive the laminate bulk properties, suchas extensional stiffness, bending-extension coupling stiffness, bendingstiffness, and the like. The laminate bulk properties may then be usedto generate a probabilistic failure envelope for the composite laminate.Such a method and system allow facility owners and operators in variousindustries to assess, support, and maintain composite laminatestructures, particularly old and aging structures, independently of theoriginal manufacturing failure information or predictions for thecomposite laminate structures. The system and method further provide theability to perform non-destructive quality assurance (QA) to ensure, forexample, that individual lamina layup was accomplished according todesign specifications.

In some embodiments, the scan data used in the above method and systemmay be ultrasonic scan data. The ultrasonic scan data may be generatedby an ultrasonic image simulator, or the scan data may be real datacaptured by an actual C-scan or equivalent type system. In otherembodiments, the scan data used in the above method and system may beacquired using X-ray signals, radio signals, acoustic signals, and thelike.

In general, in one aspect, the disclosed embodiments are directed to acomputer-aided non-destructive method of quantifying individual laminasin a composite laminate. The method comprises receiving composite scandata by a processor, the composite scan data representative of acomposite scan of the composite laminate, the composite scan dataindicating, for each one of an array of spatial locations across asurface of the composite laminate, signal intensity and signaltime-of-flight for a signal reflected and refracted off materialtransitions within the composite laminate. The method also comprisesdetermining one or more lamina properties by the processor based on thecomposite scan data, the one or more lamina properties including numberof individual laminas, fiber orientation of each individual lamina, plytype, including unidirectional or weave, weave type, and thickness ofeach individual lamina. The method further comprises calculating afailure load for the individual laminas by the processor based on theone or more a-priori known lamina moduli and failure parameters. Aprobabilistic failure envelope may then be estimated for the compositelaminate by the processor using one or more of the lamina failureparameters.

In general, in another aspect, the disclosed embodiments are directed toa computer system for non-destructive quantifying of individual laminasin a composite laminate. The computer system comprises a processor and astorage device connected to the processor. The storage device stores anapplication thereon for causing the processor to receive composite scandata into the computer system. The composite scan data is representativeof a composite scan of the composite laminate, the composite scan dataindicating, for each one of an array of spatial locations across asurface of the composite laminate, signal intensity and signaltime-of-flight for a signal reflected and refracted off materialtransitions within the composite laminate. The application stored on thestorage device also causes the processor to determine one or more laminaproperties based on the composite scan data, the one or more laminaproperties including number of individual laminas, fiber orientation ofeach individual lamina, ply type, including unidirectional or weave,weave type, and thickness of each individual lamina. The applicationstored on the storage device further causes the processor to calculate afailure load for the individual laminas based on the one or more laminaproperties. A probabilistic failure envelope for the composite laminatemay then be estimated using one or more of the lamina properties and thefailure load for the individual laminas.

In general, in yet another aspect, the disclosed embodiments aredirected to a computer-readable medium containing computer-readableinstructions for instructing a computer to perform non-destructivequantifying of individual laminas in a composite laminate. Thecomputer-readable instructions comprise instructions for causing thecomputer to receive composite scan data, the composite scan data beingrepresentative of a composite scan of the composite laminate. Thecomposite scan data indicates, for each one of an array of spatiallocations across a surface of the composite laminate, the signalintensity and signal time-of-flight for a signal reflected and refractedoff material transitions within the composite laminate. The computerreadable instructions also comprise instructions for causing thecomputer to determine one or more lamina properties based on thecomposite scan data, the one or more lamina properties including numberof individual laminas, fiber orientation of each individual lamina, plytype, including unidirectional or weave, weave type, and thickness ofeach individual lamina. The computer readable instructions furthercomprise instructions for causing the computer to calculate a failureload for the individual laminas based on the one or more laminaproperties. A probabilistic failure envelope for the composite laminatemay then be estimated using one or more of the lamina properties and thefailure load for the individual laminas.

These embodiments provide a solution that is useful in a number ofindustrial and manufacturing areas, including quality control, forexample. Other areas that may benefit from the disclosed embodiments mayinclude applications in the field of ultrasonic detector design. Stillother areas benefiting from the disclosed embodiments may be developedby those having ordinary skill in the art.

DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of the disclosed embodiments will becomeapparent from the following detailed description and upon reference tothe drawings, wherein:

FIG. 1 illustrates an exemplary system and method for characterizingcomposite laminate structures in accordance with one or more embodimentsdisclosed herein;

FIG. 2 illustrates the exemplary composite laminate characterizationsystem of FIG. 1 in more detail in accordance with one or moreembodiments disclosed herein;

FIG. 3 illustrates an exemplary laminate characterization application inaccordance with one or more embodiments disclosed herein;

FIG. 4 illustrates an exemplary ultrasonic image simulator that may beused with the laminate characterization application in accordance withone or more embodiments disclosed herein;

FIG. 5 illustrates an exemplary graphical user interface for theultrasonic image simulator in accordance with one or more embodimentsdisclosed herein;

FIG. 6 illustrates an exemplary flow chart for simulating an ultrasonicimage in accordance with one or more embodiments disclosed herein;

FIG. 7 illustrates an exemplary flowchart for detecting ply propertiesin accordance with one or more of the embodiments disclosed herein;

FIG. 8 illustrates exemplary ply thickness plots in accordance with oneor more of the embodiments disclosed herein;

FIG. 9 illustrates exemplary ply orientations in accordance with one ormore of the embodiments disclosed herein;

FIG. 10 illustrates an exemplary scatterplot and associated histogram ofply orientations in accordance with one or more of the embodimentsdisclosed herein;

FIG. 11 illustrates an unfiltered exemplary histogram and associatedscatter plot of ply orientations in accordance with one or more of theembodiments disclosed herein;

FIG. 12 illustrates the filtered version of FIG. 12 showing an exemplaryhistogram and associated scatter plot of ply orientations in accordancewith one or more of the embodiments disclosed herein;

FIG. 13 illustrates an exemplary spreadsheet and associated scatter plotof ply properties in accordance with one or more of the embodimentsdisclosed herein; and

FIG. 14 illustrates an exemplary flowchart for determining a laminatefailure envelope in accordance with one or more of the embodimentsdisclosed herein.

DESCRIPTION OF DISCLOSED EMBODIMENTS

The drawings described above and the written description of specificstructures and functions below are presented for illustrative purposesand not to limit the scope of what has been invented or the scope of theappended claims. Nor are the drawings drawn to any particular scale orfabrication standards, or intended to serve as blueprints, manufacturingparts list, or the like. Rather, the drawings and written descriptionare provided to teach any person skilled in the art to make and use theinventions for which patent protection is sought. Those skilled in theart will appreciate that not all features of a commercial embodiment ofthe inventions are described or shown for the sake of clarity andunderstanding.

Persons of skill in this art will also appreciate that the developmentof an actual, real commercial embodiment incorporating aspects of theinventions will require numerous implementation-specific decisions toachieve the developer's ultimate goal for the commercial embodiment.Such implementation-specific decisions may include, and likely are notlimited to, compliance with system-related, business-related,government-related and other constraints, which may vary by specificimplementation, location and from time to time. While a developer'sefforts might be complex and time-consuming in an absolute sense, suchefforts would nevertheless be a routine undertaking for those of skillin this art having the benefit of this disclosure.

It should also be understood that the embodiments disclosed and taughtherein are susceptible to numerous and various modifications andalternative forms. Thus, the use of a singular term, such as, but notlimited to, “a” and the like, is not intended as limiting of the numberof items. Similarly, any relational terms, such as, but not limited to,“top,” “bottom,” “left,” “right,” “upper,” “lower,” “down,” “up,”“side,” and the like, used in the written description are for clarity inspecific reference to the drawings and are not intended to limit thescope of the invention or the appended claims.

As alluded to above, the disclosed embodiments relate to a system andmethod for characterizing and quantifying a composite laminatemicrostructure. In general, the system and method may be used to derivea 3-dimensional model of the composite laminate structure, both theoverall shape and the internal structure. This 3-dimensional model,which can include and otherwise account for inherent variability andtolerances in the laminate manufacturing process, may then be used todetermine the properties and characteristics of the composite laminate.

In some embodiments, the 3-dimensional model may be generated using ascan of the composite laminate. This scan may be an ultrasonic scan insome implementations, or it may be a scan based on other types ofsignals, for example, X-ray, radio waves, sound waves, and the like. Thescan, or rather the data representing the scan, may be acquired using areal detector operating on an actual physical sample, or it may begenerated using a virtual or simulated detector instead. Thereafter,certain properties and characteristics of the composite laminate may bedetermined from the scan to allow an assessment of the compositelaminate without the need for the original or OEM (original equipmentmanufacturer) or MRO (maintenance, repair, and operations) records.

FIG. 1 illustrates an example of a composite laminate characterizationsystem 100 in accordance with the disclosed embodiments. In theexemplary embodiment of FIG. 1, the composite laminate characterizationsystem 100 is an ultrasonic system 100, although as mentioned above, anX-ray system, radio wave system, sound wave system, and the like, mayalso be used without departing from the scope of the disclosedembodiments.

Among its various functions, the laminate characterization system 100may be used to perform NDT and/or NDI on a composite laminate sample 102to determine and quantify its properties and characteristics, symbolizedby the image shown at 104. In basic operation, the composite laminatecharacterization system 100 receives scan data representing ultrasonicresponse signals that have traveled through and are subsequentlyreflected back from the composite laminate sample 102. Based on the scandata, the laminate characterization system 100 may derive and ascertaincertain information about the properties and characteristics of theplies making up the composite laminate sample 102. Such properties andcharacteristics may include, for example, the ply fiber orientation, plythickness, defect locations, and the like.

In some embodiments, the scan data for the composite laminate sample 102may be A-scans, B-scans, or C-scans. An A-scan is generally understoodto be a measure of the amplitude and flight time (or travel time) of theultrasonic signals reflected along the Z-axis (or depth direction) ofthe sample 102 over the surface (or X-Y plane) of the sample. The A-scangenerally indicates the presence of various features and defects in thesample. In graph form, the A-scan usually has the signal energydisplayed along the vertical axis and the signal flight time displayedalong the horizontal axis.

B-scans, on the other hand, provide a profile or cross-sectional sliceof the sample. In a B-scan, the graph typically displays the intensityof the returned signal as a function of depth along a linear elementwhich is typically along either the X or Y direction, displayed alongthe horizontal axis. The intensity information provides across-sectional view showing where various features and defects arelocated in that cross-section of the sample.

C-scans provide a plan or top view of specific layers or depths withinthe sample. Such scans may be used to identify the location (i.e., the Xand Y coordinates) and size of any features or defects within thesample. In graph form, this is usually displayed with the Y coordinatesalong the vertical axis and the X coordinates along the horizontal axis.C-scans are typically produced with an automated data acquisition systemand usually involve a computer controlled scanning system, or the like,to capture reflected signals at each point along a predefined grid overthe surface of the composite laminate sample.

The laminate characterization system 100 may accept scan data from areal, commercially-available ultrasonic detector 106, such as thoseavailable from US Ultratek, Inc., of Concord, Calif. An alternativeapproach may include using an A-scan system configured to translate thetransducer, or alternatively the sample being scanned, in space withscans at specific locations. These selective A-scans may then becollected in the laminate characterization system 100 to create aC-scan. The laminate characterization system 100 may also accept scandata generated by an ultrasonic image simulator for purposes of testingand validating the system. Such simulated data tends to be cleaner andmore free of noise and artifacts than real scan data from a physicalsample and therefore more useful in some cases, for example, ininitializing, configuring, and fine-tuning the laminate characterizationsystem 100.

As mentioned above, in normal operation, the laminate characterizationsystem receives an ultrasonic scan of the composite laminate sample.This scan data may indicate, for each one of an array of spatiallocations on a surface of the composite laminate sample, the signalintensity and signal time-of-flight for a signal reflecting off thelayers or plies within the composite laminate sample. The laminatecharacterization system 100 may then determine one or more propertiesfor the individual plies making up the composite laminate sample 102.Ply properties may include, for example, the number of individual plies,orientation of each individual ply, thickness of each individual ply,lamina type (unidirectional or weave), weave type, and total thicknessof the composite laminate sample. Thereafter, the laminatecharacterization system 100 may be used to calculate one or more bulkproperties for the composite laminate sample 102 given the appropriateconstitutive stiffness values of the fiber and the matrix along withtheir respective failure parameters, including extensional stiffness,bending-extension coupling stiffness, and bending stiffness, based onproperties for the individual plies (e.g., resin type, cure cycle,specific type of fiber, etc.). Once the bulk properties have beendetermined, this information may then be processed by the laminatecharacterization system 100 to estimate a probabilistic failure envelopefor the composite laminate sample 102.

In some embodiments, the laminate characterization system 100 may beimplemented as a general-purpose computer, as depicted in FIG. 1, or itmay be implemented as a dedicated computer that has been customdeveloped for the purpose. In other embodiments, the laminatecharacterization system 100 may be implemented in, or as part of, anultrasonic detector, such as the ultrasonic detector 106. This latterimplementation may produce a completely self-contained compositelaminate characterization system that can both scan a composite laminatesample and analyze its own scan data directly (i.e., no separateanalysis system is needed).

Referring still to FIG. 1, the laminate characterization system 100 isuseful for, and has applicability in, a large number of industrial andmanufacturing environments. One example where the laminatecharacterization system 100 may be particularly beneficial is insituation where information from the OEM or from an after-marketmodification on the composite stack is limited or perhaps unknown andthe as-fabricated structural characteristics (e.g., stiffness and/orfailure envelope) must be obtained without destructive testing. Anotherapplication may be in the field of quality control, for example, tocompare the as-fabricated laminate behavior with the as-designedcharacteristics. Yet another area where the laminate characterizationsystem may be useful is in ultrasonic detector design and/or selectionfor a known class of composite laminates.

FIG. 2 illustrates the exemplary laminate characterization system 100 ofFIG. 1 in more detail, including some of the components that may be usedin the system. Such a system 100 may be a conventional workstation,desktop, or laptop computer, or it may be more like a mobile or handheldsystem, or it may be a custom-developed system, such as an ultrasonicdetector that includes the additional capability discussed herein. Inthe example shown, the laminate characterization system 100 may includea bus 200 or other communication mechanism for transferring informationwithin the laminate characterization system 100, and a CPU 202 coupledwith the bus 200 for processing the information. The laminatecharacterization system 100 may also include a main memory 204, such asa random access memory (RAM) or other dynamic storage device coupled tothe bus 200 for storing computer-readable instructions to be executed bythe CPU 202. The main memory 204 may also be used for storing temporaryvariables or other intermediate information during execution of theinstructions to be executed by the CPU 202. The laminatecharacterization system 100 may further include a read-only memory (ROM)206 or other static storage device coupled to the bus 200 for storingstatic information and instructions for the CPU 202. A computer-readablestorage device 208, such as a Flash drive or magnetic disk, may becoupled to the bus 200 for storing information and instructions for theCPU 202.

The term “computer-readable instructions” as used above refers to anyinstructions that may be performed by the CPU 202 and/or othercomponents. Similarly, the term “computer-readable medium” refers to anystorage medium that may be used to store the computer-readableinstructions. Such a medium may take many forms, including, but notlimited to, non-volatile media, volatile media, and transmission media.Non-volatile media may include, for example, optical or magnetic disks,such as the storage device 208. Volatile media may include dynamicmemory, such as main memory 204. Transmission media may include coaxialcables, copper wire and fiber optics, including wires of the bus 200.Transmission itself may take the form of electromagnetic, acoustic orlight waves, such as those generated during radio frequency (RF) andinfrared (IR) data communications. Common forms of computer-readablemedia may include, for example, a floppy disk, a flexible disk, harddisk, magnetic tape, other magnetic medium, a CD ROM, DVD, other opticalmedium, a RAM, a PROM, an EPROM, a FLASH EPROM, other memory chip orcartridge, or any other medium from which a computer can read.

The CPU 202 may also be coupled via the bus 200 to a display 210 fordisplaying information to a user. One or more input devices 212,including alphanumeric and other keyboards, mouse, trackball, cursordirection keys, and so forth, may be coupled to the bus 200 forcommunicating information and command selections to the CPU 202. Acommunications interface 214 may be provided for allowing the laminatecharacterization system 100 to communicate with an external system ornetwork.

In accordance with the disclosed embodiments, a laminatecharacterization application 216, or rather the computer-readableinstructions therefor, may also reside on or be downloaded to thestorage device 208. The laminate characterization applicationsubstantially embodies the concepts and principles of theearlier-mentioned laminate characterization application in the form of aspecific software application developed using a particular programminglanguage. Such a software application may then be executed by the CPU202 and/or other components of the laminate characterization system 100to analyze and characterize the structure of composite laminatematerials, as will be discussed further herein.

The programming language used to implement the laminate characterizationapplication 216 may be any suitable programming language known to thosehaving ordinary skill in the art, and the application may be developedin any suitable application development environment known to thosehaving ordinary skill in the art. Examples of programming languages mayinclude MATLAB (from The MathWorks, Inc.) and LabVIEW (from NationalInstruments, Inc.), as well as C, C++, FORTRAN, and Visual Basic and thelike.

Referring now to FIG. 3, in one embodiment, the laminatecharacterization application 216 may comprise a number of discretefunctional components, including a data acquisition component 300, a plydetection component 302, and a failure prediction component 304.Although not specifically shown, a graphical user interface (GUI) mayalso be present in some embodiments for allowing users to interact withand provide input to one or more of the functional components. Otherfunctional components may also be part of the laminate characterizationapplication 216 without departing from the scope of the disclosedembodiments. Note that although the functional components of thelaminate characterization application 216 have been depicted asindividual components in FIG. 3, those having ordinary skill in the artwill understand that two or more of these components may be combinedinto a single component, and that any individual component may bedivided into several constituent components, or omitted altogether,without departing from the scope of the disclosed embodiments.

In general operation, the data acquisition component 300 functions toreceive and process scan data into the laminate characterizationapplication 216 for characterization and testing of a given compositelaminate sample. This scan data may come from an ultrasonic imagesimulator, as described further below, or from a real ultrasonicdetector. In either case, the data acquisition component 300 may alsoprocess the scan data in some embodiments, including scrubbing andcleaning the data as needed of any extraneous or unwanted input, such asnoise and artifacts from the ultrasonic detector. In some embodiments,instead of a single pulse for a given location, several pulses (e.g., 5to 20) of the same location may be taken, then the signals are averagedtogether.

An example of an ultrasonic image simulator that may be used with thelaminate characterization application 216 in some embodiments isdepicted in FIG. 4. As can be seen, the ultrasonic image simulator 400,like the laminate characterization application 216, may be composed ofseveral functional components, including an ultrasonic detectorsimulator 402 and a composite geometry simulator 404. As before, otherfunctional components may also be part of the ultrasonic image simulator400 without departing from the scope of the disclosed embodiments. Thecomposite material data needed to conduct the simulation may be providedfrom one or more readily available composite material database 406 orother sources. In general, the ultrasonic detector simulator 402operates to emulate real ultrasonic response signals, while thecomposite geometry simulator 404 generates the geometries of a compositelaminate sample. These two functional components operate together toproduce ultrasonic scans, or rather the data representing the scans, ofthe composite laminate samples.

In some embodiments, the ultrasonic image simulator 400 may beconfigured to simulate ultrasonic response signal from a C-scan orC-scan equivalent detector in pulse-echo mode (though it is alsopossible for the ultrasonic image simulator 400 to operate inthrough-transmission mode). The ultrasonic image simulator 400 mayaccomplish this by using standard or known theories for 1-dimensionalsound wave propagation within an attenuating medium (see, e.g., Schmerr,L. W., Fundamentals of Ultrasonic Nondestructive Evaluation, 1998,Plenum Press; Lonne et al., Review of Quantitative NondestructiveEvaluation, 2004, pp. 875-882). An acoustic pulse within an attenuatingmedium will generate a refraction and reflection wave whenever thereexists a material boundary, such as occurs within the CFRP as the wavepasses between the resin rich regions and the impregnated carbon fibers.In accordance with the disclosed embodiments, the ultrasonic imagesimulator 400 can generate ultrasonic C-scan images for variousindustrial ply types over a wide range of defects, includingmisalignments during layup, voids due to manufacturing limitations, andintentionally fabricated holes such as for mounting the component.

The scan data may then be analyzed by the ply detection component 302.In some embodiments, the ply detection component 302 does this byanalyzing each time integration point (where time is directly correlatedto depth within the laminate) and using an appropriate mathematicalimage reconstruction mechanism to capture the primary directions of theply. In some embodiments, the Radon transform, Hough transform, anEigensystem analysis, Fast Fourier transform, and the like may be usedto determine the fiber principal directions and thus the fiberorientation directions of a given laminate. Each C-scan is integrated inX and Y directions to produce a bulk signal for a given depth in thelamina (as shown in the examples in FIG. 8). The overall laminathickness is determined by the time of flight of the signal to the backwall of the lamina. Individual ply thickness is determined by the timeof flight between the individual peaks in the bulk signal. Theeigenvectors generally correspond to the alignment direction of the plyat a given depth, and the ratio of the transform peaks generallycorrespond to whether the ply is unidirectional (i.e., this would beanalogous to when the first eigenvalue is much higher than the secondeigenvalue, and could also be found using classical eigenvalue analysis)or is a woven fabric (i.e., when the transform peaks are of similarmagnitude) where the ratio implies the degree of warp within anindividual ply.

In some embodiments, the stack thicknesses and ply orientation is thenused with the results from the ply detection component 302 along withthe constitutive material properties of the matrix and reinforcement toobtain the structural stiffness tensor using known laminate theories(see, e.g., R. M. Jones, Mechanics of Composite Materials, SecondEdition, New York, Taylor and Francis, 1999 (“Jones”), where in thepresent configuration the lamina stiffness is obtained using thewell-known Tandon-Weng theory (see Tandon, G. P. and G. J. Weng, TheEffect of Aspect Ratio of Inclusions on the Elastic Properties ofUnidirectionally Aligned Composites, Polymer Composites, 5(4):327-333,1984 (“Tandon-Weng”)) with the closed form solution implied by Tuckerand Liang (see Tucker, C. L. and E. Liang, Stiffness Predictions forUnidirectional Short-Fiber Composites: Review and Evaluation, CompositesScience and Technology, 59:655-671, 1999 (“Tucker and Liang”)) forunidirectional laminas. There exist a host of many alternativemicromechanical methods to predict the ply stiffness response once theunderlying constitutive ply makeup is understood, and the above are justunderstood to be one of the better alternative schemes. It is of coursepossible and known to analyze the stack thicknesses and fiberorientation for hybrid and non-hybrid woven fibers as well asunidirectional fibers. See, e.g., Scida et al., Elastic behaviorprediction of hybrid and non-hybrid woven composite, Comp. Science andTechnology, 1997, 57:1727-1740 (“Scida”).

If the manufacture-supplied stiffness (“C”) and/or compliance (“S”)tensors (one is the inverse of the other) is provided, the stiffness ofa unidirectional laminate in the principal material directions may befound from the constitutive materials. On the other hand, if aunidirectional ply is assumed, only the properties of the constitutivematerials are needed, such as the isotropic stiffness of the epoxy andthe transversely isotropic stiffness tensor of the carbon fibers. Thesevalues may be used as taught in Tandon-Weng, to return the effectivestiffness of the lamina using a unidirectional plane stressapproximation. Another option is the outdated, but industrially-acceptedmethod discussed in Halpin, J. C. and J. L. Kardos., The Halpin-TsaiEquations: A Review, Polymer Engineering and Science, 16(5):344-352,1976 (“Halpin-Tsai”), or as discussed in Tucker and Liang, the moreaccurate approach of Mori, T. and K. Tanaka, Average Stress in Matrixand Average Elastic Energy of Materials with Misfitting Inclusions, ActaMetallurgica, 21:571-574, 1973 (“Mori-Tanaka”), of using the approachoutlined in Tandon-Weng. Both approaches require knowledge of theYoung's modulus and Poisson Ratio of the fiber, E_(f) and v_(f),respectively, and the matrix, E_(m) and v_(m). In addition, they requirethe volume fraction of fibers V_(f) and the effective aspect ratio ofthe individual fibers within the tows a_(r). Completion of thesecalculations return the stiffness and compliance tensors, along with thedesired planar Young and Shear Moduli and Poisson's Ratios, E₁₁, E₂₂,G₁₂, G₂₃, v₁₂, and v₂₃, which could alternatively be obtained directlyfrom the components of S. This tensor can then be rotated into thecomposite coordinates using standard tensor rotations. Once theunderlying stiffness tensor for a given lamina is understood, any of avariety of classical laminate theories may be used to predict thefabricated composite's stiffness components. See, e.g., Barbero, E. J.,Introduction to Composite Materials Design, Second Edition, 2011(“Barbero”); Jones.

The individual lamina failure envelopes may thereafter be used by thefailure prediction component 304 to generate a failure envelope for thecomposite laminate, once the ply stiffness is known and the materialfailure parameters of the matrix and fiber are known. This may beaccomplished using any of the industrially-accepted techniques, such asthe Tsai-Wu failure criteria. See, e.g., Tsai, S. W., and Wu, E. M., Ageneral theory of strength for anisotropic materials, J. Compos. Mater.,5, pp. 58-80 1971 (“Tsai-Wu”); see also Jones or Barbero. In general,the Tsai-Wu criteria may be used to generate the failure envelope of thelamina, and that information may then be used with ply failure theoriesto predict the failure of the laminate. Unlike traditional approachesthat assume the load is planar, the failure prediction component 304 canhandle a generalized 6-dimensional loading condition, including 3different mutually orthogonal normal stresses and 3 different mutuallyorthogonal shearing stresses. In some embodiments, the failure envelopesof the composite laminates may be analyzed assuming a degree ofuncertainty within the stack, such as the ply orientation, and theprobabilistic failure envelopes may be generated using a Monte-Carloapproach. See, e.g., Vo, T. and D. A. Jack, Structural Predictions ofPart Performance for Laminated Composites, 2011 ECTC Proceedings. Thisapproach allows characterization of a probabilistic confidence of theactual failure envelope of the as-processed composite laminate based onthe uncertainties in the ply detection algorithm.

The above embodiments are particularly useful for modifiers of compositestructures who do not have direct access to original manufacturing,operations, maintenance and repair information. QA personnel who providevarious composite structure quality assurance services where the OEMinformation is typically available may also find the disclosed laminatecharacterization system beneficial. In general, the laminatecharacterization system can help provide: detailed comparison ofas-manufactured to as-designed composite structures; detailedcharacterization of initial state load carrying capability; detailedcharacterization of use or age related intra-lamina issues; reduction orelimination of so-called “coupon” or sample testing requirements;reduction in margins of safety in design leading to reduced weight forcomposite end items; the ability to independently and non-destructivelyvalidate composite material stack up without OEM or MRO design ormanufacturing records; and the ability to certify a modified compositestructure or structural repair without OEM design or load informationusing an equivalent strength methodology.

Detector Considerations

With respect to the types of detectors that may be used, the majorparameters that affect an ultrasonic pulse within a medium are the speedof sound within a particular material and the optical impedance of thematerial, defined as the material density multiplied by the local speedof sound. Also of interest is the type of wave generated by thedetector. There are typically two types of waves of interest in NDT,plane waves and shear waves. Both types will be present within any givenmaterial, but depending on the detector configuration one or both typesmay be captured. Some detectors use a fluidic interface between thedetector and the material being sampled, and thus due to the inabilityof shear waves to pass through a fluidic media, these detectors are bestused in a pulse-wave dominated configuration using a pulse-echo methodwhere a single transducer is used as both a transmitter and a receiveror in a through transmission mode where one transducer is placed on eachside of the object of interest. The signal will be scattered whenever achange in the acoustic impedance (often defined loosely as the materialdensity times speed of sound) changes within a structure, thus whenevera beam passes between the matrix and a tow, a signal will be scatteredand the objective of NDT is to capture and interpret this signal.

A third parameter of interest is the attenuation of the signal's poweras a function of frequency. In graphite composites, for example, thespeed of sound is in a range near 3 mm/μs. At 10 MHz, the cycle time fora single wavelength is 0.1 μs or 100 ns and the corresponding wavelengthis 0.3 mm. Thus, the cycle time for an individual wavelength must beless than or equal to the sensor gate (integration) time to avoid errorsin detected signal amplitude due to partial wave integrations.

Pulse-wave detectors function by sending out a pulse and waiting for theechoes from the changing impedance of the target material. The variablesof interest for these detectors are the ‘z-start’ and ‘z-gate’ times.The z-start time is the time at which the detector starts to detect andintegrate the echoed signal in the z-axis (equivalent to the depth), andthe z-gate time is the period during which the detector is integratingor “listening” to the echoed signal. These times correspond,respectively, to the initial depth and thickness of the lamina beingtest. For example, using a 10 MHz signal in a CFRP laminate, a z-startof 0 and a z-gate of 1.0 μs corresponds to an image that starts at thelaminate's surface and produces an echoed signal from the first 3 mm ofmaterial. Sub-microsecond z-gates and frequencies greater than 10 MHzare therefore necessary to detect fiber tows with typical thicknesses of0.214 mm. A 20 MHz detector with a 50 ns z-gate would allow atheoretical resolution of 0.145 mm.

The detector resolution is also a function of the ultrasonic image'spixel resolution, with each pixel representing the smallest discretespatial location that can be assessed for a given composite laminatesample. A typical pixel may be about 0.21 mm in the X and Y directions(i.e., length and width) for high end commercially availablecharacterization systems, corresponding to a signal having about a 20MHz frequency. The choice of frequency is a trade-off between spatialresolution of the image and imaging depth. Lower frequencies produceless resolution, but penetrate deeper into a sample. Higher frequencieshave a smaller wavelength and thus are capable of reflecting orscattering from smaller structures, but have a larger attenuationcoefficient and thus the signal is more readily absorbed by the plies,limiting the penetration depth of the signal.

Following is a more detailed description of some of the methods,assumptions, and procedures used with the laminate characterizationapplication 216 in accordance with some embodiments, beginning withoperation of the ultrasonic image simulator 400.

Geometric Simulation

As mentioned with respect to FIG. 4, in some embodiments, the ultrasonicimage simulator 400 may include a composite geometry simulator 404configured to provide the geometry of a laminate. The composite geometrysimulator 404 takes as inputs the areal density, fiber tow width, andwarp percentage to establish the spacing of the fibers for a givenlamina in the X and Y directions (i.e., length and width). Thisinformation may be provided, for example, from a composite materialdatabase 406 and the like and includes the ply material thickness. Thecomposite geometry simulator 404 then builds a 3-dimensional matrix oflayers by orienting individual fibers to the layer angle of orientationinput by the user. Because fiber placement is usually not rigorouslycontrolled to sub-tow width, the composite geometry simulator 404randomly adjusts the starting fiber position for each layer (i.e., sothe fibers will not typically lay perfectly on top of one another in theX and Y directions even for layers having the same orientation). Inaddition, depending on manufacturing technique, fiber orientation is notperfect, and the composite geometry simulator 404 may be configured tosimulate such imperfection. Specifically, the composite geometrysimulator 404 may simulate fiber orientations from the followingprocesses: machine layup (almost no orientation variability fromplanned), machine assisted layup (about 0.8 degrees standard deviationfrom planned), and hand layup (about 4 degrees standard deviation fromplanned).

In addition, the composite geometry simulator 404 may also be configuredto simulate voids between the individual layers of the laminate. In theassembly of individual layers, air can become trapped, leading to anepoxy void between layers. In real applications, these voids effectivelyabsorb the ultrasonic pulse so that the layers below these voids are notdetected. Typical values of voids are 1% to 2% by volume of thecomposite laminate. The geometry simulator allows for the introductionof these voids and can simulate them randomly between layers. The voidshave material properties of air and can be made ellipsoid in shape andvary randomly in size, X, Y and interlayer position. Void volumes areuser selectable between 0%, 1%, 1.5%, 2%, or more by volume.

The composite geometry simulator 404 also has the ability to introducedrilled holes of various diameters and X and Y positions. These also aresimulated with material properties of air, but unlike the voids, thesecontinue through all layers.

Finally, the composite geometry simulator 404 allows the user tosimulate a rectangular insert of a different material property betweenselected layers. In practice, these inserts are typically made of Teflonor similar material. The rectangular area is simulated by assigning thedesired materials density and associated speed of sound in the geometrymatrix where desired. The purpose of this rectangular insert is tosimulate a large scale “flaw” in the material that, unlike the voidsdiscussed above, does not cause an ultrasonic signal to be completelyabsorbed by the flaw, so continued detection beneath this material ispossible. The insert may then be used as a way to properly calibrate X,Y and Z resolution.

Ultrasonic Detector Simulation

In general, the ultrasonic detector simulator 402, which may bedeveloped using MATLAB or other similar programming language, makes useof well-known NDT fundamentals (see, e.g., Schmerr, L. W., Fundamentalsof Ultrasonic Nondestructive Evaluation, Plenum Press, 1998)(“Schmerr”). This ultrasonic detector simulator 402 may be for a generalmultidimensional signal with both plane and shear waves, or it may besimplified for a 1-D pulse-echo assumption (no shear waves). Such anultrasonic detector simulator 402 may then be used to provide asimulation of an ultrasonic C-scan for a composite laminate.

In the present embodiment, each discrete spatial location (i.e., pixel)in the ultrasonic C-scan, the ultrasonic detector simulator 402 usesknowledge of the location of the transition between each layer as wellas the material properties (e.g., speed of sound, material density,etc.) of the layer from the geometric simulator. The governingdifferential equations of an acoustic medium are then solved numericallyto simulate an ultrasonic wave translating within the part at anindividual spatial location. The resulting intensity solution as afunction of time is typically stored in an array for each spatiallocation in the simulated scan, such that each spatial location isassociated with a separate array.

The ultrasonic detector simulator 402 also uses inputs for the waveintensity at the initial surface. Using an Ordinary DifferentialEquation (ODE) solver, the wave front may be computed as a function oftime. Although an ODE solver is not needed to determine how long ittakes for a wave to pass between the layers, the ODE solver has anadditional benefit in that signal attenuation may be readilyincorporated. The full analysis for the wave propagation is notdescribed in detail here, as it may be readily obtained from standardNDT textbooks, including Schmerr.

Care should be taken when the wave enters a boundary andreflects/refracts, as the equations that capture reflection/refractionbehavior between layer transitions involving pure epoxy and epoxy/fiberlayers (see, e.g., Equations (6.157)-(6.168) of Schmerr) for an incidentp-wave (a.k.a., the elastic wave of the pressure wave, often attributedto compression effects) and the s-wave (a.k.a. the shear wave or thesecondary wave, often attributed to the change in shape of an object)assume that the interface between layers is represented by amathematically continuous contact. This is appropriate when there isperfect (or near perfect) bonding between the fiber and the resin.

The intensity of each wave is a function of the amplitude of thepressure pulse, density of the material, the speed of sound of thematerial, and attenuation behavior of the medium. Using Equations(6.7)-(6.16) of Schmerr, the ultrasonic detector simulator 402 is ableto properly account for the intensity of every individual ray within thelaminate.

In some of the lower quality embodiments, the ultrasonic detectorsimulator 402 assumes an ideal material where there is no signalattenuation within the medium, although this may not be realistic forhigher frequencies (e.g., greater than 10 MHz), as it is known that asthe frequency of the incident signal increases, polymeric materials tendto damp out the signal. An additional feature of the ultrasonic detectorsimulator 402 is the ability to tailor the intensity cutoff, thusmimicking the physical threshold of the physical detector. In general,the more layers exist within a laminate, the more independent rays willexist within the composite due to the bounce-between of the rays betweenlayers. The more a ray bounces between layers and splits into areflected and refracted wave, the weaker the signal becomes.

The current ultrasonic detector simulator 402 also performspost-processing to analyze the dependence of the returned signal outputfor both pulse duration, Δt_(Power Pulse), and z-gate width,Δt_(z-gate). For example, if the detector pulse were left on too long orhad a long ring time after the initial pulse, it would be impossible todistinguish the returned signal from individual layers. The z-gate widthis also a significant consideration as a z-gate value that is too largewill capture the return signal from multiple layers. The smaller thez-gate, the greater the accuracy of the detector, but this comes at areduction in the total intensity and thus could impose on thresholdlower limits.

In some embodiments, the ultrasonic detector simulator 402 may simulatecertain physical detectors, which do not return the signal as a functionof time. Instead, the ultrasonic detector simulator 402 may return theaverage intensity of the signal as a function of time through a formsimilar to:

$\begin{matrix}{{\overset{\_}{I}\left( {t_{{z - {{gate}\mspace{14mu} {start}}},}\Delta \; t_{z - {gate}}} \right)} \equiv {\frac{1}{\Delta \; t_{z - {gate}}}{\int_{t_{z - {{gate}\mspace{14mu} {start}}}}^{t_{z - {{gate}\mspace{14mu} {start}}} + {\Delta \; t_{z - {gate}}}}{{I\left( {t,{\Delta \; t_{{Power}\mspace{14mu} {Pulse}}}} \right)}{t}}}}} & (1)\end{matrix}$

where Ī(t_(z-gate start), Δt_(z-gate)) is the average intensity at agiven start time and will depend on the entered z-gate width. This valueis often reported at a certain depth for a homogeneous material, butthis description will be somewhat ambiguous as the “depth” of a signalis a function of the material impedance (density multiplied by the speedof sound). In the case of a composite laminate, this cannot be knowna-priori as the material in question has a spatially varying materialmake-up and even the choice of matrix hardener have impact significantlythe resulting speed of sound of the material.

Graphical User Interface

FIG. 5 illustrates an example of a graphical user interface (GUI) thatmay be provided with the ultrasonic detector simulator 402. As can beseen, in some embodiments, the user is provided with the option toselect type of detector, which will establish the resolution of theultrasonic scan to be output. The highest resolution provided by thesimulated detector has 0.1 mm resolution in the X and Y axes andsingle-lamina resolution in the Z direction. Examples of availableselections for “real” detectors include the Imperium I-600 detector with0.21 mm resolution in the X and Y direction and Z resolution controlledby various frequency ranges and z-gate timing from 2.7 MHz-20 MHz.

Another user input choice is “manual” or “material database.” If“manual” is selected, then the user may input the individual parametersmanually. Selection of “material database” allows a user to select froma database of materials listing the available composite material data.The user may then select a material and the data therefor will beautomatically loaded into the ultrasonic detector simulator 402.

An example of the data contained in the material database is provided inTable 1 below for various plies in several common composite laminates.These configurations were obtained from various handbooks andmanufacturers databases, and are provided as typical examples oflaminate stacks. Other sources may include the MIL-17 handbook series“Composite Materials Handbook,” which contains the effective stiffnesstensor data for a wide variety of military standard laminas.

TABLE 1 Material Properties Aereal Tow Fiber Ply Num of Name DensityWarp % Width Volume Thickness Plys Cytec 7714A T650-35 195 0.5 0.3760.54 0.2 18 Cytec 7714A M461 195 0.95 0.394 0.54 0.2156 15 Cytec 7714ASHST-35 380 0.5 0.75 0.57 0.429 10 FiberCole T300 SHS 6K 380 0.5 0.750.57 0.429 10 Cytec 7740 T650-35-35-PW-195-4 195 0.5 0.376 0.54 0.2 18

Once a material is loaded, the user selects the z-gate width and z-gatestart for output display. In perfect detector mode, this selection isaccomplished in layer units and the z-gate step is in single layers. Insimulated detector modes, this input is in millimeter for all threevalues and z-gate width is limited to unit wavelengths which is afunction of the selected detector frequency.

The user may then select assembly methods, flaw sizes, holes and holepatterns, and the Teflon insert. Once all of these selections are made,the ultrasonic detector simulator 402 generates a series of C-scanimages at different depths throughout the simulated laminate anddisplays the result. The user may then view the laminate at variousdepths by selecting the appropriate layer. The user may also selectdifferent z-gate widths and step sizes to produce an updated simulation.Simulations of different flaw sizes and detector types, or changes inmaterial selections, may also be updated and recalculated. Once theultrasonic detector simulator 402 has produced the simulated C-scans,the results can be saved for subsequent processing.

FIG. 6 illustrates the operation of the ultrasonic image simulator 400described above in the form of a flowchart 600. As can be seen,operation of the ultrasonic image simulator 400 begins, including of thegeometry of the composite laminate being simulated at block 602 a,including spatial information for fiber tows and sound properties forfiber and resin, and the like, and defining the properties of theultrasonic emitter/detector being simulated, including signal intensity,sensitivity, frequency, waveform length, waveform shape, and the like,at block 602 b is. At block 604, for every spatial position (i.e.,pixel) on the composite laminate, the ultrasonic image simulator 400solves the equations of transmission for the intensity observed by adetector.

Then, at block 606, the ultrasonic image simulator 400 numericallysolves (e.g., using ODE techniques) spatial and temporal form of wavetransmission equations of motion for signal intensity spectrum as afunction of time. These equations may be found, for example, in Lonne,S., A. Lhemery, P. Calmon, S. Biwa, and F. Thevenot, Modeling ofUltrasonic Attenuation in Unidirectional Fiber Reinforced CompositesCombining Multiple-Scattering and Viscoelastic Losses, in review ofQuantitative Nondestructive Evaluation, editors D. O. Thompson and D. E.Chimenti, pp. 875-882, published by American Institute of Physics, 2004(“Lonne”). Specifically, Lonne provided plots that suggested anattenuation characteristic within a composite laminate. A mathematicalform may be used for attenuation, as follows, Attn=10^(−(af+b)Δx/20),where f is the frequency, a and b are experimentally observedcoefficients, and Δx is the distance covered by a pulse in a given timeof interest.

At block 608, the ultrasonic image simulator 400 retains the intensitysplit as a pulse passes between layers and lends itself to a reflectionand refraction pulse. At block 610, from the 1-dimensional solution, theultrasonic image simulator 400 retains surface return intensity (bothfront and back surface for, respectively, pulse-echo and throughtransmission), as this represents the A-scan signal observed by adetector. Once the above operations have been performed for everyspatial position (i.e., pixel) on the composite laminate, then at block612, the ultrasonic image simulator 400 compiles the A-scans from eachspatial location into a spatially resolved image of the returnedintensity at a moment in time. These compiled A-scans results comprisethe C-scan images that are subsequently provided to the ply detectioncomponent 302 for further analysis (see FIG. 7).

Ply Detection Process

Continuing with embodiments of the invention, data representing theC-scan images of the composite laminate, whether from an actual detectoror simulated as described above, is provided to the ply detectioncomponent 302 for further processing. Actual detector data, of course,means the analysis is being performed on a real composite laminatesample, whereas simulated data may be more beneficial for purposes oftesting and fine tuning the operation of the ply detection component302.

FIG. 7 generally illustrates the operation of the ply detectioncomponent 302 in the form of a flowchart 700, beginning with block 702,where A-scans with 10 ns or less timing and less than 0.25 mm spacing inthe X and Y direction are acquired, either from a real detector or froman ultrasonic simulator (see FIG. 6.), for a composite laminate. The plydetection component 302 uses these A-scans to generate C-scan sliceswith 10 ns steps or increments and 10 ns z-gates at block 704 byintegrating the A scan amplitude data over the timing gate relative tothe initiation of the reflected signal which signifies the front face ofthe laminate. In this way, the timing from all A scans represents thesame depth within the laminate producing a slice across the laminate ata known depth. At block 706, the ply detection component 302 processesthe C-scan slices using filters, thresholding and morphologicalfeatures. These filters include normalizing the signal and applyingvarious top and bottom thresholds to remove noise or saturated signalswhich would cause inaccuracies in the image transforms. When identifyingweave types, various linear and 2-dimensional morphological filters areused to pass or remove signals prior to final image transforms. At block708, the ply detection component 302 uses the bulk C-scan amplitudesignal as shown in FIG. 8 to determine the number of plies, the widthper ply, and the total laminate thickness using bulk image properties.

At block 710, the ply detection component 302 again generates C-scanslices using the A-scans, except that these C-scan slices are about athird of the individual ply thickness from the front wall to 1.3 timesthe laminate stack thickness. This is done to insure a given slicerepresents the “center” of a ply and is therefore not compromised by theply above or the ply below. These C-scan slices are again processedusing filters, thresholding, and linear morphological features at block712. At block 714, the ply detection component 302 applies one ofseveral possible 2-dimensional transforms and thresholding to the C-scanslices to determine their primary and secondary orientations. Primaryorientations are the highest resultant transform signal and secondaryorientations are the second highest transform signal from the filteredresults as shown in FIG. 9 for a simulated weave. Examples of2-dimensional transforms that may be used include the well-known Radontransform, Hough transform, Eigensystem analysis, the Fast FourierTransform (FFT), and the like.

Once the primary and secondary orientations are determined, as at block716, the ply detection component 302 uses the orientations to determinewhether each C-scan slice is a weave or unidirectional. Thisdetermination is performed by first filtering the orientation data toremove outliers, and overlapping plies, at block 718. At block 720, theply detection component 302 uses the previously determined ply thicknessto apply a timing mask corresponding to the predicated steps for eachindividual ply. The ply detection component 302 thereafter usesstatistical techniques to determine the most likely ply orientation bylooking at a histogram of most likely ply angles for the stepsassociated with a given ply mask and type (e.g., weave, unidirectional,etc.) from the remaining data, at block 722. By statistically buildingup data from all slices in a given ply, a most probable determinationcan be made. With the information on the number of plies, ply thickness,and ply orientation now available, a failure envelope may be determinedfor the composite laminate.

Operation of the ply detection component 302 discussed above was studiedover a range of possible ply examples. For these examples, a narrowz-step size (10 ns) and a narrow z-gate (100 ns) was used to createapproximately 15 images per ply for thin plies and approximately 30images per ply for thick plies. These numbers provided sufficientstatistical data to determine a final ply orientation. The studyproduced an output of the bulk image properties as a function of z-stepsize, similar to that shown in FIG. 8. In the figure, the ply thicknessoutput for a 10-ply stack is shown in the plot on the left, where thevertical axis represents C-scan amplitude and the horizontal axisrepresents the number of z-steps being made. The result is a smoothedplot of the bulk response showing peaks at several steps, with the laststep being the back wall. The plot on the right shows the number ofplies as determined by the number of first derivative zero crossings,plus 1 zero crossing assumed for the first layer.

Once the number of plies is determined and the total thickness isdetermined, the number of z-steps being made per ply may be determined.The number of z-steps per ply and initial z-step showing signal (wherez-gate plus z-step crosses the boundary from ply 1 to ply 2) allows fora mask to be used to isolate the plies. In the example shown in FIG. 8,this is about 17 z-steps per ply. Ply number 2 information is providedbetween z-steps 8 and 24. Ply number 3 information is between z-steps 25and 41, and so forth.

FIG. 9 is an example of the ply orientation for the example of FIG. 8,corresponding to ply number 1 (zero degrees orientation) and ply number2 (10 degrees orientation). In this example, the plot on the left side,with the vertical axis representing Radon amplitude and the horizontalaxis representing orientation in degrees, was derived using a modifiedRadon function, where various filters were applied with an orientationfrom 0 to 180 degrees for detection. In that plot, the right peak (Peak1, at about 100 degrees) represents the primary orientation and the leftpeak (Peak 2, at about 10 degrees), represents the second reorientation.The image on the right is the C-scan output of the ultrasonic detectorsimulator 402 corresponding to the Radon image on the left. As can beseen, the plot on the left shows the primary and secondary fiberorientation peaks for each z-step. From this left plot, an orientationmay be determined. If the two peaks are roughly 90 degrees out of phasewith each other and of roughly the same magnitude, a determination maybe made that this represents a weave. The z-step here indicates a weavefiber pattern because, although a unidirectional fiber can show twopeaks, the primary and secondary peaks are usually on top of each other.The ply type (weave or unidirectional) may therefore be determinedautomatically in some embodiments.

FIG. 10 shows an example of a scatterplot (left-hand plot) of determinedprimary and secondary orientations from z-steps 8 through 24. Thisscatterplot shows either a 10 degree or 100 degree orientation, with thehorizontal axis representing z-step number, and the vertical axisrepresenting angles in degrees, and circles represent the primaryorientation and squares represent the secondary orientation. Using thehistogram approach on the primary and secondary peaks, the right plotshows the output determination for ply number 2—a weave with primaryorientation 10 degrees and secondary orientation 100 degrees—where thehorizontal axis is angles in degrees, and the vertical axis is the countcorresponding to the primary and secondary angles from each step in theleft-hand plot).

A filter may be applied to determine the orientations that representreal signals versus noise, as may be shown in the illustrative examplesof FIGS. 11 and 12. In these figures, the left-hand plots are similar tothe plot shown in FIG. 10, while the right-hand plots have the z-stepsalong the horizontal axis and ply orientation angles along the verticalaxis. FIG. 11 is the unfiltered histogram for a unidirectional case withpossible ply orientations 0, 30, 60, 90, 120, and 150 degrees (for a 0to 180 degree orientation), and FIG. 12 is the filtered histogramshowing the determined possible orientations.

The final results for the ply detections may be presented, for example,in the form of a spreadsheet similar to the one shown in FIG. 13, whichis being provided for illustrative purposes only. The examplespreadsheet shows some of the relevant ply information and a graphicshowing the detected ply orientation as a function of z-step. In thisexample, the spreadsheet includes the ply number (first column fromleft), the calculated ply orientation (second column), actualorientation (third column), and ply type (e.g., unidirectional, weave,etc.) (fourth column). The fifth and six columns show the averagecomputed thickness and average actual thickness for the plies,respectively. These results may then be provided to the failureprediction component 304 to be used for probabilistic failure envelopedetermination.

The foregoing failure prediction operation is set forth in FIG. 14 interms of a flow chart 1400. Beginning at block 1402, the failureprediction component 304 receives the ply orientation after step 722 ofFIG. 7, ply type and thickness from the ply detection component 302. Anyuncertainty or variability as a function of the detector type may alsobe inputted or signed at this time in the form of the stochasticdistribution or in terms of the mean and variance of the input. At block1404, the material properties (either the fiber and matrix moduli,failure parameters, packing density, and fabric type, or theexperimentally obtained or manufacture supplied lamina stiffness tensorand failure parameters) for the composite laminate sample may be definedor otherwise provided to the failure prediction component 304 along withtheir uncertainties.

Thereafter, the failure protection component randomly samples a set ofproperties for each layer of each probabilistic parameter, which mayinclude orientation, fiber stiffness tensor, matrix stiffness tensor,ply thickness, ply type (weave type or unidirectional), fiber volumefraction, porosity, and so forth, at block 1406. At block 1408, thefailure prediction component 304 generates the bulk laminate stiffnessmatrix from the constitutive materials' properties. This may be doneusing well-known laminate theory (see, e.g., Jones) and may beprobabilistic in nature. The failure prediction component 304 thenselects a planar loading scenario and linearly increase each loadvariable until failure occurs, at block 1410. Possible failure theoriesthat may be used here include Tsai-Wu and Tsai-Hill, as both werediscussed in K-S Liu, S. W. Tsai, A Progressive Quadratic failurecriterion for nonlinear analysis of composite laminates subjected tobiaxial loading, Composites Science and Technology, 1998 58:1107-1124(“Liu and Tsai”); A. Puck, H. Schurmann, Failure analysis of frplaminates by means of physically based phenomenological model,Composites Science and Technology, 58(7), 1045-1067 (“Puck andSchurmann”); and the like.

Once failure is identified for a given loading scenario, the failureprediction component 304 repeats the process for each possible planarloading scenario for full failure envelope at block 1412. At block 1414,the failure prediction component 304 returns to block 1406 and thisprocess is repeated for a sufficient number of samples to identify asmooth form for the probabilistic failure curve. If a smoothrepresentation of the probabilistic failure curve is obtained, then theresults are analyzed at block 1416. The analysis may involve, from aquality control perspective, using use the envelope to quantify theprobability of failure for an in-service part under a known (eitherdeterministic or probabilistic) load, at block 1418. Alternatively, atblock 1420, the analysis may involve, from a design perspective,expanding the failure curve sufficiently to encompass an acceptablepercentage of failure loads for a replacement or supplemental part.

Such an arrangement is particularly useful for modifiers of compositestructures who do not have direct access to original manufacturing,operations, maintenance and repair information. QA personnel who providevarious composite structure quality assurance services where the OEMinformation is typically available may also find the disclosed laminatecharacterization system beneficial.

The foregoing embodiments can characterize and quantify compositelaminate structures. These embodiments take a composite laminate ofunknown ply stack composition and sequence and determine variousinformation about the individual plies, such as ply stack, orientation,microstructure, and type. The embodiments can distinguish between weavetypes that may exhibit similar planar stiffness behaviors, but wouldproduce considerably different failure mechanisms. The information aboutthe plies may then be used to derive the laminate bulk properties fromexternally provided constitutive properties of the fiber and matrix,such as extensional stiffness, bending-extension coupling stiffness,bending stiffness, and the like. The laminate bulk properties may thenbe used to generate a probabilistic failure envelope for the compositelaminate. This allows facility owners and operators in variousindustries to assess, support, and maintain composite laminatestructures, particularly old and aging structures, independently of theoriginal manufacturing failure information or predictions for thecomposite laminates structures. The embodiments further provide theability to perform non-destructive quality assurance to ensure, forexample, that individual lamina layup was accomplished according todesign specifications, and results can be used to identify a wide rangeof laminate properties beyond purely structural.

While the disclosed embodiments have been described with reference toone or more particular implementations, those skilled in the art willrecognize that many changes may be made thereto without departing fromthe spirit and scope of the description. Each of these embodiments andobvious variations thereof is contemplated as falling within the spiritand scope of the claimed invention, which is set forth in the followingclaims.

What is claimed is:
 1. A computer-aided non-destructive method ofquantifying individual laminas in a composite laminate, the methodcomprising: receiving composite scan data by a processor, the compositescan data representative of a composite scan of the composite laminate,the composite scan data indicating, for each one of an array of spatiallocations across a surface of the composite laminate, signal intensityand signal time-of-flight for a signal reflected and refracted offmaterial transitions within the composite laminate; determining one ormore lamina properties by the processor based on the composite scandata, the one or more lamina properties including number of individuallaminas, fiber orientation of each individual lamina, ply type,including unidirectional or weave, weave type, and thickness of eachindividual lamina; calculating a failure load for the individual laminasby the processor based on the one or more a-priori known lamina moduliand failure parameters; and estimating a probabilistic failure envelopefor the composite laminate by the processor using one or more of thelamina failure parameters.
 2. The method according to claim 1, whereindetermining one or more lamina properties by the processor comprisesprocessing the composite scan data using filters, thresholding, andmorphological features.
 3. The method according to claim 1, wherein thefiber orientation of each individual lamina is determined by theprocessor using a mathematical transform to identify a primary fiberorientation and a secondary fiber orientation indicative of across-stitched weave for each individual lamina.
 4. The method accordingto claim 3, wherein the mathematical transform may be one of thefollowing: a Radon transform, a Hough transform, an Eigensystemanalysis, and a Fast Fourier transform.
 5. The method according to claim3, further comprising determining by the processor whether eachindividual lamina is unidirectional or weave based on the primary fiberorientation and secondary fiber orientation of each individual lamina.6. The method according to claim 1, wherein the composite scan data isultrasonic C-scan data.
 7. The method according to claim 1, wherein thecomposite scan data is one of the following: data simulated by asimulated ultrasonic C-scan, and data acquired by a real ultrasonicdetector.
 8. A computer system for non-destructive quantifying ofindividual laminas in a composite laminate, the computer systemcomprising: a processor; a storage device connected to the processor,the storage device storing an application thereon for causing theprocessor to: receive composite scan data into the computer system, thecomposite scan data representative of a composite scan of the compositelaminate, the composite scan data indicating, for each one of an arrayof spatial locations across a surface of the composite laminate, signalintensity and signal time-of-flight for a signal reflected and refractedoff material transitions within the composite laminate; determine one ormore lamina properties based on the composite scan data, the one or morelamina properties including number of individual laminas, fiberorientation of each individual lamina, ply type, includingunidirectional or weave, weave type, and thickness of each individuallamina; calculate a failure load for the individual laminas based on theone or more lamina properties; and estimate a probabilistic failureenvelope for the composite laminate using one or more of the laminaproperties and the failure load for the individual laminas.
 9. Thecomputer system according to claim 8, wherein the processor determinesthe one or more lamina properties by processing the composite scan datausing filters, thresholding, and morphological features.
 10. Thecomputer system according to claim 8, wherein the fiber orientation ofeach individual lamina is determined by the processor using amathematical transform to identify a primary fiber orientation and asecondary fiber orientation indicative of a cross-stitched weave foreach individual lamina.
 11. The computer system according to claim 10,wherein the mathematical transform may be one of the following: a Radontransform, a Hough transform, an Eigensystem analysis, and a FastFourier transform.
 12. The computer system according to claim 10, theprocessor determines whether each individual lamina is unidirectional orweave based on the primary fiber orientation and secondary fiberorientation of each individual lamina.
 13. The computer system accordingto claim 8, wherein the composite scan data is ultrasonic C-scan data.14. The computer system according to claim 8, wherein the composite scandata is one of the following: data simulated by a simulated ultrasonicC-scan, and data acquired by a real ultrasonic detector.
 15. Acomputer-readable medium containing computer-readable instructions forinstructing a computer to perform non-destructive quantifying ofindividual laminas in a composite laminate, the computer-readableinstructions comprising instructions for causing the computer to:receive composite scan data, the composite scan data representative of acomposite scan of the composite laminate, the composite scan dataindicating, for each one of an array of spatial locations across asurface of the composite laminate, signal intensity and signaltime-of-flight for a signal reflected and refracted off materialtransitions within the composite laminate; determine one or more laminaproperties based on the composite scan data, the one or more laminaproperties including number of individual laminas, fiber orientation ofeach individual lamina, ply type, including unidirectional or weave,weave type, and thickness of each individual lamina; calculate a failureload for the individual laminas based on the one or more laminaproperties; and estimate a probabilistic failure envelope for thecomposite laminate using one or more of the lamina properties and thefailure load for the individual laminas.
 16. The computer-readablemedium according to claim 15, wherein the computer-readable instructionscause the computer to determine one or more lamina properties byprocessing the composite scan data using filters, thresholding, andmorphological features.
 17. The computer-readable medium according toclaim 15, wherein the computer-readable instructions cause the computerto determine the fiber orientation of each individual lamina by using amathematical transform to identify a primary fiber orientation and asecondary fiber orientation indicative of a cross-stitched weave foreach individual lamina.
 18. The computer-readable medium according toclaim 17, wherein the mathematical transform may be one of thefollowing: a Radon transform, a Hough transform, an Eigensystemanalysis, and a Fast Fourier transform.
 19. The computer-readable mediumaccording to claim 17, wherein the computer-readable instructions causethe computer further to determine whether each individual lamina isunidirectional or weave based on the primary fiber orientation andsecondary fiber orientation of each individual lamina.
 20. Thecomputer-readable medium according to claim 15, wherein the compositescan data is ultrasonic C-scan data.
 21. The computer-readable mediumaccording to claim 15, wherein the composite scan data is one of thefollowing: data simulated by a simulated ultrasonic C-scan, and dataacquired by a real ultrasonic detector.